I was asked to make an 11X15 sheet cake to feed 40 people as a farewell cake. I normally charge $3.00 a slice of cake for wedding and birthdays. But since a sheet cake is different, I am not sure of what to charge them.   Would someone please give me some guidance?  Thank you in advance.

Market rate is specific to area.  Where I live, wedding cakes start at $9/serving; catering starts $125/per plate; photography average is $5.000; venue average $12,000.  

You will need to research market rate in your area; then calculate your costs and profit margin from there.

In general a sheet cake is the same as a birthday cake.......your pricing is *very!* low.  I suggest you check on the pricing of cakes at any local grocery store or 'stand alone' bakery to see what the 'going price' is in your area then probably up that by $5.   It's hard to say because you have not posted any pix of your work so we don't know your skill level.........maybe you do super great special cakes but maybe you are only a 'newby'.  I don't mean that in a nasty way....just trying to point out that pricing depends somewhat on skill level.

Thank you all for the comments I will check in my area to see what the various cake pricing.   I haven't posted any of my cakes on this forum but I've posted many on Facebook.  I will post some soon.  Thank you again.